Successful Implementation of a New Method of Analyzing Tropospheric Peroxy Radicals

Peroxy radicals play very important roles in the atmosphere. For example, when peroxy radicals react with nitric oxide, they lead to the formation of ozone. The ACD/NCAR PerCIMS instrument has successfully quantified the peroxy radicals HO2 and HO2 plus RO2 in field measurement campaigns, but the previous method had not allowed rapid change between the two measurement quantities. New research has lead to a method of measuring both values within one minute. The key breakthrough involved modulation of the concentration ratio of nitric oxide to oxygen within the instrument inlet.Laboratory and atmospheric sample data using this new method are shown in Figures 1 and 2, respectively. The laboratory data show measurement of a 50:50 mixture of HO2 and CH3O2 in the HO2 mode (orange) and the HO2+RO2 mode (blue). Other points are background signals. The ambient data show measurements of HO2+RO2 (blue) and HO2 (pink) as well as the ratio of HO2 to HO2+RO2 (green). This analytical method will be applied in several field campaigns in 2006.